diff --git a/neutron_lib/api/definitions/__init__.py b/neutron_lib/api/definitions/__init__.py
index 9dcfe9550..347d4fb2e 100644
--- a/neutron_lib/api/definitions/__init__.py
+++ b/neutron_lib/api/definitions/__init__.py
@@ -62,7 +62,9 @@ from neutron_lib.api.definitions import l3
 from neutron_lib.api.definitions import l3_conntrack_helper
 from neutron_lib.api.definitions import l3_ext_gw_mode
 from neutron_lib.api.definitions import l3_ext_ha_mode
+from neutron_lib.api.definitions import l3_ext_ndp_proxy
 from neutron_lib.api.definitions import l3_flavors
+from neutron_lib.api.definitions import l3_ndp_proxy
 from neutron_lib.api.definitions import l3_port_ip_change_not_allowed
 from neutron_lib.api.definitions import logging
 from neutron_lib.api.definitions import logging_resource
@@ -188,7 +190,9 @@ _ALL_API_DEFINITIONS = {
     l3_conntrack_helper,
     l3_ext_gw_mode,
     l3_ext_ha_mode,
+    l3_ext_ndp_proxy,
     l3_flavors,
+    l3_ndp_proxy,
     l3_port_ip_change_not_allowed,
     logging,
     logging_resource,
diff --git a/neutron_lib/api/definitions/base.py b/neutron_lib/api/definitions/base.py
index 2838e8517..53f1dee89 100644
--- a/neutron_lib/api/definitions/base.py
+++ b/neutron_lib/api/definitions/base.py
@@ -24,6 +24,7 @@ KNOWN_ATTRIBUTES = (
     'device_owner',
     'dns_nameservers',
     'enable_dhcp',
+    'enable_ndp_proxy',
     'fixed_ips',
     'gateway_ip',
     'host_routes',
@@ -110,6 +111,8 @@ KNOWN_EXTENSIONS = (
     'l3-conntrack-helper',
     'l3-ha',
     'l3_agent_scheduler',
+    'l3-ext-ndp-proxy',
+    'l3-ndp-proxy',
     'l3-port-ip-change-not-allowed',
     'logging',
     'metering',
diff --git a/neutron_lib/api/definitions/l3_ext_ndp_proxy.py b/neutron_lib/api/definitions/l3_ext_ndp_proxy.py
new file mode 100644
index 000000000..ceacb9c53
--- /dev/null
+++ b/neutron_lib/api/definitions/l3_ext_ndp_proxy.py
@@ -0,0 +1,48 @@
+# Copyright (c) 2020 Troila.
+# All rights reserved.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+from neutron_lib.api import converters
+from neutron_lib.api.definitions import l3
+from neutron_lib.api.definitions import l3_ext_gw_mode
+from neutron_lib import constants
+
+
+ALIAS = 'l3-ext-ndp-proxy'
+IS_SHIM_EXTENSION = False
+IS_STANDARD_ATTR_EXTENSION = False
+NAME = 'Router support to enable NDP proxy'
+API_PREFIX = ''
+DESCRIPTION = 'Router extension to enable ndp proxy'
+UPDATED_TIMESTAMP = '2020-08-25T00:00:00-00:00'
+RESOURCE_NAME = l3.ROUTER
+COLLECTION_NAME = l3.ROUTERS
+ENABLE_NDP_PROXY = 'enable_ndp_proxy'
+RESOURCE_ATTRIBUTE_MAP = {
+    COLLECTION_NAME: {
+        ENABLE_NDP_PROXY: {
+            'allow_post': True,
+            'allow_put': True,
+            'convert_to': converters.convert_to_boolean_if_not_none,
+            'default': constants.ATTR_NOT_SPECIFIED,
+            'is_visible': True,
+            'is_filter': True
+        }
+    }
+}
+SUB_RESOURCE_ATTRIBUTE_MAP = {}
+ACTION_MAP = {}
+REQUIRED_EXTENSIONS = [l3.ALIAS, l3_ext_gw_mode.ALIAS]
+OPTIONAL_EXTENSIONS = []
+ACTION_STATUS = {}
diff --git a/neutron_lib/api/definitions/l3_ndp_proxy.py b/neutron_lib/api/definitions/l3_ndp_proxy.py
new file mode 100644
index 000000000..c1cce9e29
--- /dev/null
+++ b/neutron_lib/api/definitions/l3_ndp_proxy.py
@@ -0,0 +1,128 @@
+# Copyright (c) 2020 Troila.
+# All rights reserved.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+from neutron_lib.api.definitions import l3
+from neutron_lib.db import constants as db_const
+
+# The alias of the extension.
+ALIAS = 'l3-ndp-proxy'
+
+# Whether or not this extension is simply signaling behavior to the user
+# or it actively modifies the attribute map.
+IS_SHIM_EXTENSION = False
+
+# Whether the extension is marking the adoption of standardattr model for
+# legacy resources, or introducing new standardattr attributes. False or
+# None if the standardattr model is adopted since the introduction of
+# resource extension.
+# If this is True, the alias for the extension should be prefixed with
+# 'standard-attr-'.
+IS_STANDARD_ATTR_EXTENSION = False
+
+# The name of the extension.
+NAME = 'L3 NDP Proxy'
+
+# A prefix for API resources. An empty prefix means that the API is going
+# to be exposed at the v2/ level as any other core resource.
+API_PREFIX = ''
+
+# The description of the extension.
+DESCRIPTION = "Router support for L3 NDP proxy."
+
+# A timestamp of when the extension was introduced.
+UPDATED_TIMESTAMP = "2021-06-29T10:00:00-00:00"
+
+# The name of the resource.
+RESOURCE_NAME = 'ndp_proxy'
+
+# The plural for the resource.
+COLLECTION_NAME = 'ndp_proxies'
+
+ID = 'id'
+NAME = 'name'
+PROJECT_ID = 'project_id'
+ROUTER_ID = 'router_id'
+PORT_ID = 'port_id'
+IP_ADDRESS = 'ip_address'
+DESCRIPTION = 'description'
+
+# The resource attribute map for the extension.
+RESOURCE_ATTRIBUTE_MAP = {
+    COLLECTION_NAME: {
+        ID: {'allow_post': False,
+             'allow_put': False,
+             'validate': {'type:uuid': None},
+             'is_visible': True,
+             'is_sort_key': True,
+             'primary_key': True},
+        NAME: {'allow_post': True,
+               'allow_put': True,
+               'validate': {'type:string': db_const.NAME_FIELD_SIZE},
+               'is_filter': True,
+               'is_sort_key': True,
+               'is_visible': True, 'default': ''},
+        PROJECT_ID: {'allow_post': True,
+                     'allow_put': False,
+                     'required_by_policy': True,
+                     'validate': {
+                         'type:string': db_const.PROJECT_ID_FIELD_SIZE},
+                     'is_sort_key': True,
+                     'is_visible': True},
+        ROUTER_ID: {'allow_post': True,
+                    'allow_put': False,
+                    'validate': {'type:uuid': None},
+                    'is_sort_key': True,
+                    'is_visible': True},
+        PORT_ID: {'allow_post': True,
+                  'allow_put': False,
+                  'validate': {'type:uuid': None},
+                  'is_sort_key': True,
+                  'is_visible': True},
+        IP_ADDRESS: {'allow_post': True,
+                     'allow_put': False,
+                     'default': None,
+                     'validate': {
+                         'type:ip_address_or_none': None},
+                     'is_sort_key': True,
+                     'is_visible': True},
+        DESCRIPTION: {'allow_post': True,
+                      'allow_put': True,
+                      'default': '',
+                      'validate': {'type:string':
+                                   db_const.LONG_DESCRIPTION_FIELD_SIZE},
+                      'is_visible': True}
+    }
+}
+
+# The subresource attribute map for the extension. It adds child resources
+# to main extension's resource. The subresource map must have a parent and
+# a parameters entry. If an extension does not need such a map, None can
+# be specified (mandatory).
+SUB_RESOURCE_ATTRIBUTE_MAP = {}
+
+# The action map: it associates verbs with methods to be performed on
+# the API resource.
+ACTION_MAP = {
+}
+
+# The action status.
+ACTION_STATUS = {
+}
+
+# The list of required extensions.
+REQUIRED_EXTENSIONS = [l3.ALIAS]
+
+# The list of optional extensions.
+OPTIONAL_EXTENSIONS = []
diff --git a/neutron_lib/plugins/constants.py b/neutron_lib/plugins/constants.py
index 4f65fabff..aa8a4001d 100644
--- a/neutron_lib/plugins/constants.py
+++ b/neutron_lib/plugins/constants.py
@@ -31,3 +31,5 @@ PLACEMENT_REPORT = "placement_report"
 #               retired (train) and these should no longer be necessary.
 LOADBALANCER = "LOADBALANCER"
 LOADBALANCERV2 = "LOADBALANCERV2"
+
+NDPPROXY = 'NDPPROXY'
diff --git a/neutron_lib/tests/unit/api/definitions/test_l3_ext_ndp_proxy.py b/neutron_lib/tests/unit/api/definitions/test_l3_ext_ndp_proxy.py
new file mode 100644
index 000000000..6d3c374ca
--- /dev/null
+++ b/neutron_lib/tests/unit/api/definitions/test_l3_ext_ndp_proxy.py
@@ -0,0 +1,20 @@
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+from neutron_lib.api.definitions import l3_ext_ndp_proxy
+from neutron_lib.tests.unit.api.definitions import base
+
+
+class RouterNDPProxyDefinitionTestCase(base.DefinitionBaseTestCase):
+    extension_module = l3_ext_ndp_proxy
+    extension_attributes = ('enable_ndp_proxy',)
diff --git a/neutron_lib/tests/unit/api/definitions/test_l3_ndp_proxy.py b/neutron_lib/tests/unit/api/definitions/test_l3_ndp_proxy.py
new file mode 100644
index 000000000..e10fcf812
--- /dev/null
+++ b/neutron_lib/tests/unit/api/definitions/test_l3_ndp_proxy.py
@@ -0,0 +1,23 @@
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+from neutron_lib.api.definitions import l3_ndp_proxy
+from neutron_lib.tests.unit.api.definitions import base
+
+
+class L3NDPProxyDefinitionTestCase(base.DefinitionBaseTestCase):
+    extension_module = l3_ndp_proxy
+    extension_resources = (l3_ndp_proxy.COLLECTION_NAME,)
+    extension_attributes = (l3_ndp_proxy.ID, l3_ndp_proxy.NAME,
+                            l3_ndp_proxy.PROJECT_ID, l3_ndp_proxy.ROUTER_ID,
+                            l3_ndp_proxy.PORT_ID, l3_ndp_proxy.IP_ADDRESS,
+                            l3_ndp_proxy.DESCRIPTION,)
diff --git a/releasenotes/notes/l3-ndp-proxy-71eee0cba8565dad.yaml b/releasenotes/notes/l3-ndp-proxy-71eee0cba8565dad.yaml
new file mode 100644
index 000000000..6a255d20d
--- /dev/null
+++ b/releasenotes/notes/l3-ndp-proxy-71eee0cba8565dad.yaml
@@ -0,0 +1,6 @@
+---
+features:
+  - |
+    The ``l3-ndp-proxy`` and ``l3-ext-ndp-proxy`` API definitions are
+    introduced, which allow a router to support proxy NDP for IPv6
+    addresses of internal ports.